The invention relates to a device for sealing an annular gap between a housing and a shaft supported in the housing.
German Patent Application DE 38 26 628 shows a prior art example of such a device. The device seals the annular gap both to prevent the escape of lubricants and to prevent the admission of impurities. In the device in German Patent Application DE 38 26 628, a first sealing lip is prestressed radially against an inner ring, in a customary manner. A second sealing lip also abuts against the inner ring, and a third sealing lip strikes against a radial section of the inner ring, the sealing lips acting as a labyrinth seal. The space between the first and the second sealing lips contains a grease packing.
Such devices are also described as cartridge seals, and they are needed when shafts with radial toothing on the front end must be guided axially through a sealing ring already inserted in the housing, and the more cost-effective rotary shaft lip seals (without an inner ring) are not usable because the danger would exist that their sealing lips would be damaged by the shaft during assembly. The comparatively soft sealing members are endangered in the case of a device without an inner ring, especially in the case of a shaft constructed at the front end as a spline shaft.
In the case of a device in accordance with the generic concept as in German Patent Application DE 38 26 628, this danger of damage to the sealing lips does not exist. Nevertheless, such a device still has a number of disadvantages.
Since the second sealing lip abuts against the inner ring only because of its inherent elasticity, the escape of grease from the space between the first and the second sealing lips cannot be completely prevented. By the rotation of the inner ring, the grease is accelerated to move toward the outside via the radial flange section and the shorter generally cylindrical section, without the third sealing lip being able to prevent it to any appreciable extent. The escaping grease not only constitutes irretrievable loss of lubricant from the system, but also pollutes the environment.
When the grease supply is used up, the second and third sealing lips operate without lubrication. This, sooner or later, leads to their destruction, both because of friction and because of heating which occurs to temperatures intolerable for the rubber material of the sealing lips.
A similar effect also occurs when, because of pressure differences developing during operation, the grease supply moves toward the inside via the first sealing lip. In this case, the third sealing lip operates without lubrication from the start, and the second sealing lip operates without lubrication as soon as only a small portion of the grease has moved toward the inside.